In packaging machines, especially vacuum packaging machines or gas flushed packaging machines, a product is placed on a bottom web of material and covered by a top web. The space between these webs is evacuated or subjected to a gas flushing, and then the webs are welded together and sealed around the product. In some cases, the bottom web is thermoformed to form receiving trays for the product. The webbing material is unwound from a reel which is mounted on the packaging machine. From the reel, the webbing material passes around a number of rollers before it reaches the packaging station. When the material on a reel runs out, it is necessary to replace the existing reel with a new reel, and manually thread the leading portion of the material from the new reel to the packaging station. This operation is time consuming, and leads to a reduction in the productivity of the packaging machine.
EP-A-0179243 discloses an apparatus designed to overcome these problems. The machine supports two reels of webbing material, the webbing material from each reel being guided by a plurality of rollers to a sheet-holder. A separate sheet-holder is provided for each web of material, and the two sheet-holders are arranged in a V-shaped configuration with the surface over which the webbing material runs on each sheet-holder facing the other. In this case, webbing from one reel is supplied over one sheet-holder to a downstream packaging machine, whilst the leading edge of material from the other reel is held on the opposed sheet-holder. As the reel from which material is supplied to the packaging machine is exhausted, the trailing edge is severed by a severing means provided on the sheet-holder, and the sheet-holder is pivoted thereby pressing the trailing edge of the sheet of webbing material onto the leading edge of webbing material held on the other sheet-holder. The two sheets are spliced by use of a pressure sensitive adhesive provided on one sheet. On separation of the opposed sheet-holders, material from the full reel is supplied to the packaging machine. The exhausted reel is then replaced by a new, full reel of webbing material, and operation of the packaging machine continues with no substantial delay for reel changing.
In practice, machines of this type have not enjoyed commercial success. The arrangement shown in EP-A-0179243 requires pressure sensitive adhesive on the leading edge of material to be applied on opposite sides for alternating reels, or for a user to manually add adhesive when the material is held by the sheet-holder. If adhesive is put on the wrong side, the two sheets of webbing material will not join and the new reel of material must be manually fed through to the packaging machine, this being very time consuming.
EP-A-0445333 discloses an apparatus for feeding plastic film for a bag making machine. As with the system of EP-A-0179243, the trailing edge of one reel is joined to the leading edge of a second reel. The problem of adhesive being applied to the wrong side of material on the reel is avoided as the reels are provided on a rotatable arm which rotates about 180.degree. when reels are changed. This ensures material in the wait position is always arranged with the adhesive surface facing the same direction. The disadvantage of this system is that, for packaging machines, the reels are typically of a large diameter and therefore a system in which a supporting arm is rotated requires a large area to operate. This area is generally not available for commercial packaging lines.
Another option which has been proposed is to join two rolls of webbing material by welding rather than using an adhesive. This has not been generally accepted as a commercially useful method, due to technical problems and cost considerations.